Power grids have developed rapidly around the world with the development of economy. There has been an increasing demand for various components used in the power grids, and insulators are among the rest. Insulators are used to support transmission lines, and may ensure sufficient insulation between the transmission lines and the crossarm and the tower. In operation, the insulators should be capable of withstanding the vertical load and the horizontal tension of the transmission lines. The insulators are also exposed to the sun and rain, and are subject to the change of weather and corrosion of chemicals. Therefore, the insulators are required to have both excellent electrical performances and sufficient mechanical strength. The quality of insulators is critical to the safe operation of the transmission lines.
Insulators can be classified by structure as supporting insulator, suspension insulator, anti-pollution insulator and bushing insulator. Commonly used in overhead lines are pin insulator, shackle insulator, suspension insulator, porcelain crossarm, rod insulator, strain insulator, etc. Electrical faults of insulators include flashover and breakdown. Flashover occurs in the surface of the insulator, with visible burn marks but normally without damaging the insulation; breakdown occurs in the interior of the insulator by discharging through the porcelain between an insulator cap and an insulator pin, possibly damaging the insulation but without any marks in the appearance, and also possibly destroying the insulator completely due to an electric arc. For breakdown, the insulator pin should be examined for the discharging mark and the burn mark.
Currently, disk-type multi-piece suspension insulators are often used, as shown in FIG. 1. FIG. 2 illustrates one single piece of FIG. 1. As shown in FIG. 2, the single piece comprises a socket 1, an umbrella 11 and a head 9. A plurality of (e.g., n in FIG. 1) single-pieces are connected in series to form the structure in FIG. 1. Conventional suspension insulators are made of porcelain or glass, and especially, porcelain insulators have existed for more than 100 years. However, porcelain or glass has a high density, which imposes a heavy load to the tower.